The idea is that Christians state a certain part of the bible is true. They do not claim it is metaphorically, allegorically, symbolically, etc. They claim it is literally true. Take a look at this before you continue reading:
http://www.religioustolerance.org/chr_inte.htm
Anwyay, a Christian will claim something like "God hates homosexuality because it says so in Leviticus." In this case, the Christian is not looking at metaphors; they are being literal! At this point, it is fair to ask the Christian if they also believe if people should be executed for homosexual. The Christian will most likely answer 'no', but they would be ignoring the part in Leviticus that says they must be executed. In fact, it is the very next sentence after the abomination part!
Also, homosexuals are executed in Iran, where they do not cherry-pick their religious beliefs. As such, it is fair to accuse Christians as being cherry-pickers, because they pick and choose which parts are literal, which are literal, and which parts they ignore completely.
By the way, an atheist can tell you how to interpret the bible. All I have to do is consult a scholarly resource on the various methods of bible interpretation. As I already pointed out, "hermeneutics" is a valid field of study. You might wish to look into it.